This invention relates to a nut assembly used to secure an instrument by use of a bolt to a structure, the back of which is not accessible.
A conventional nut assembly 1 of this type is shown in FIGS. 8A-11. It comprises a frame 9 having a flange 7 formed with a bolt hole 6, two elongated flat arms 8 extending parallel to each other in one direction from both sides of the flange 7 and each formed with elongated holes 10, and a nut 5 substantially in the shape of a rectangular pole having four longitudinal sides.
A pair of pins 3 protrude laterally from a pair of opposed longitudinal sides of the nut 5 and are loosely received in the elongated holes 10 of the arms 8 so that the nut 5 is pivotable about the pins 3 relative to the arms 8. The arms have lugs 12 at their distal ends. The nut 5 has lugs 11 adapted to abut the lugs 12 when the nut 5 longitudinally aligns with the arms 8 to prevent the nut 5 from turning in one direction from this position while allowing it to turn only in the opposite direction from this position by 90xc2x0. Further, the lugs 11 and 12 are arranged such that the nut 5 is slidable in the holes 10 only while the nut 5 is positioned perpendicular to the arms 8.
The nut 5 is formed with a threaded hole 2 extending therethrough from one of the second pair of opposed longitudinal sides to the other. The nut 5 is further formed with an inclined guide surface 4 arranged such that when a bolt A is inserted through the bolt hole 6 with the lugs 11 and 12 in abutment with each other, the bolt slides along the guide surface 4 while pivoting the nut 5 in the opposite direction until the nut becomes perpendicular to the axis of the arms 8 and its threaded hole 2 aligns with the bolt hole 6.
The flange 7 of the frame 9 is substantially rectangular and is formed with a cylindrical apron wall 13 (FIG. 8B) extending in the same direction as the arms 8 from the edge of the bolt hole 6 to guide the bolt A toward the threaded hole 2 of the nut 5.
In order to guide the bolt axially toward the threaded hole 2, the cylindrical apron wall 13 has an inner diameter slightly greater than the major diameter of the bolt
At one end of the threaded hole 2 where the guide surface 4 is formed, an inverted conical guide hole 14 is formed coaxially and communicating with the threaded hole 2 to guide the bolt smoothly into the threaded hole.
FIGS. 9 and 10 show how this nut assembly is used to secure an article C to a board B whose back is inaccessible. First a starting hole D is formed in the board B with such a size that with the lugs 11 and 12 in abutment with each other, the nut 5 and the arms 8 can pass therethrough but the flange 7 cannot The nut assembly is inserted into the hole D with the lugs 11 and 12 in abutment with each other until the flange 7 abuts the edge of the hole D. Then, with an article C to be fastened to the board B pressed against the flange 7, a bolt A is inserted through a hole E of the article C and the hole D of the board B and slid along the guide surface 4 until the nut 5 pivots about the pins 3 and becomes perpendicular to the axis of the arms 8.
In this state, the threaded hole 2 of the nut 5 aligns with the bolt hole 6. Thus, as the bolt A is turned by a screwdriver in this state, it threads into the threaded hole 2 while pulling the nut 5 toward the flange 7 until the nut 5 is pressed against the back of the board B as shown in FIG. 9. The article C is now fastened to the board B.
In the example shown, the board B is fairly thick, so that the apron wall 13 is not received in the guide hole 14. But if the board B is thinner, the former will be received in the latter. Thus, the diameter of the guide hole 14 at its top has to be at least slightly greater than the outer diameter of the apron wall 13, that is, it has to be at least slightly greater than the sum of the major diameter of the bolt A and twice the thickness of the wall 13. Thus, the maximum diameter of the guide hole 14 at its top is substantially greater than the major diameter of the bolt A. On the other hand, in order to minimize the diameter of the starting hole D, the thickness and width of the nut 5 have to be as small as possible. Thus, the portions of the nut between the side edges of the nut and the side edges of the guide hole 14 are small in width T1 as shown in FIG. 8A. Since these portions are narrow, the nut tends to bend or buckle at these portions as shown in FIG. 11 when the bolt is tightened. Once the nut bends or buckles, it is impossible to tighten the bolt any further.
In order to accurately guide the bolt toward the threaded hole 2, the apron wall 13 has to be sufficiently long in the longitudinal direction. But it was technically difficult to form a long cylindrical wall by pressing the flange 7. Thus, the conventional apron wall 13 was too short to guide the bolt
An object of the invention is to provide a nut assembly having a pivotable nut that is less likely to be bent, buckled or otherwise damaged and capable of guiding a bolt accurately.
According to the invention, there is provided a nut assembly with a pivotable nut comprising a nut having a threaded through-hole and a pin on each side thereof, and a frame having a flange formed with a bolt hole and a pair of arms provided on both sides thereof so as to extend in one direction, the arms each being formed with an elongated hole, the nut being formed at one end thereof with an inclined guide surface for pivoting the nut when pushed by a bolt, the nut being pivotally and slidably mounted between the arms with the pins received in the elongated holes in the arms, characterized in that a pair of hanging walls extending in a direction in which a bolt is inserted are provided around the bolt hole at two portions so as to oppose each other in an imaginary plane perpendicular to a line connecting the pins on the nut
The hanging walls may have the distance between them decreasing gradually toward their tips.
The hanging walls may have their circumferential ends terminating at positions inside of edges of the arms.